The present invention relates to apparatus for converting a first specified input video signal of a first pixel and line rate to a second specified output video signal of a second pixel and line rate. Specifically, the apparatus captures and digitizes a still frame video image from the incoming video signal and reformats the image and any included alphanumeric overlay to conform to a second video format specification.
Shortly after the invention of television, a video standard (NTSC) was adopted for use by manufacturers of home video or consumer video electronics products. Among other specifications, the standard defines the number of picture elements (pixels) composing a line, the number of horizontal lines composing a video frame, and the sequence and rate of transmitting the lines. As a result of the NTSC standard in the United States and the PAL standard in Europe, commercial televisions, video cameras and video tape recorders based on a given standard are mutually compatible and capable of interchanging images by means of analog signals.
Today, many specialized computer-based imaging devices are unable to adopt the earlier video standards as a video output format because their still frame video images are defined by more pixels per line, more lines per frame, or require a higher transmission rate than that specified by existing standards. Among applications for these specialized video signals are Landsat imaging, computer-based medical imaging, computerized image printing, computer graphics, computer aided design, and non-destructive product testing and inspection. Their non-standard video output signal specifications render them incompatible with each other and with any of the more widely available standardized equipment such as video tape recorders, laser image printers, closed circuit video cable networks and video transmission systems.
This invention is designed to adapt the specialized, non-standard video output signals and image formats to either a specified video standard signal or any other non-standard video specification and image format for the purpose of compatibility or interconnection of the respective sending and receiving devices. Acting in this capacity, the apparatus may function as a video interface, as a remote image acquisition system, or as a front-end image processor for a laser film recorder. The invention is especially useful in medical imaging systems.
There are currently five (5) major medical imaging modalities that produce diagnostic images from computer processing of data produced by specialized sensing techniques. They are Computerized Axial Tomography (CAT), Magnetic Resonance Imaging (MRI), Ultrasound (US), Nuclear Medicine (NM), Digital Radiography (DR), specifically Digital Chest (DC), and Digital Subtraction Angiography (DSA). Most ultrasound devices produce NTSC standard video because they were intentionally designed to store their image information on commercial video tape recorders. However, the other modalities were intentionally designed to display more pixels per line and more lines per frame, and at higher transmission rates in order to present the maximum amount of image information on their respective display screens and to avoid distracting screen flicker. These non-standard video specifications are a result of placing primary design emphasis on medical diagonosis, at the expense of compatibility with each other, with any standardized video equipment, and with certain other valuable peripheral devices.
However, secondary to the principal desire to produce a diagnostic quality screen display of the images, imaging professionals would like to be able to transfer the non-standard images to peripheral archiving, printing and telecommunications devices. Among the most desirable applications for such peripherals are video tape archiving for subsequent review, laser recording of the images on film also for archiving and subsequent review, and telephone transfer of the images to another site for redisplay and confirmation of the diagnosis.
It is currently difficult or impossible to connect most medical imaging devices to video tape recorders, laser film recorders and so-called teleradiology systems either by digital or video interfacing techniques because of the inherent incompatibility of the host computers and video output specifications of these devices. Therefore, these three examples are immediate and principal applications for the invention based on its ability to convert the non-standard video outputs of the medical imaging devices to the requirements of any otherwise incompatible peripheral or video device.
In one such application of the invention, non-standard high resolution images produced by CAT, MRI, NM, DC and DSA could be acquired directly from the imaging devices, converted to the NTSC standard and archived on a video tape recorder. In a second application, similarly acquired images could be converted and transferred by the apparatus to a laser film recorder for printing. In a third application, the apparatus could convert and then transfer such acquired images to a teleradiology system for communication to a distant site. In these last two applications, the apparatus can either convert the images to the appropriate video specification or digital format and subsequently transfer them to the receiving device as either a video output or transfer them across a digital bus as a digital output. Current methods of interfacing medical imaging devices directly to laser film recorders and teleradiology systems, including digital interface and customized video interfaces, produce less than desirable results. The current methods of digital connection by means of direct serial or parallel interfaces are generally cumbersome to use, unable to accommodate alphanumeric overlays without significant distortion, slow in performance, expensive and functional only in limited cases. The current direct video interfaces are generally based on modifications of standard video digitizers. Although they are easier to use, their performance is often imprecise. Cropped image, linear distortions, predictable pixel duplications throughout the image, damaged alphanumerics and other difficulties are commonly seen.
For the teleradiology application, an indirect method of image transfer is currently being used. It is based on the use of a standard video camera connected to a standard video digitizer incorporated in the teleradiology system. The medical images are first transferred photographically to transparency film. The transparency-based image is then backlit by a lightbox, and photographed by the video camera The camera's standard video output is then digitized by the teleradiology system's video digitizer.
The use of the present invention is easier and more accurate than the indirect video method, and the image quality resulting from the use of the apparatus is far superior Another way of improving the digitizing process includes laser scanners which are inherently capable of much higher resolution than can be used in the teleradiology application and thus must be supported by computer systems that can reduce the data to the requirements of the teleradiology video.
A principal motivation of the present invention is the ability to reformat and transmit images during a patient examination due to its nature of being connected on-line to the imaging system. More effective consultations can be conducted as additional images can be produced during the present patient examination.